This invention relates to disc shaped optical record carriers, such as CDs, DVDs and their combination, so-called hybrid discs. Various standards for CDs and DVDs in respect to their different formats and also in respect to their dimensions are known.
For example the standard ECMA-130 in respect to data interchange on read-only 120 mm optical data discs (CD-ROM) defines the dimensions of the centre hole, the clamping area and the rim area of CD-ROMs comparable to the general specification of CDs. Here all diameters are referred to the centre of the centre hole or to reference planes P and Q, with reference plane P as to be the plane on which the bottom surface of the clamping area, i.e. on the read-out side of the disc, rests and reference plane Q the parallel plane to reference plane P at the height of the top surface of the clamping area, i.e. on the label side of the disc.
In particular, the centre hole shall have a cylindrical shape and its diameter shall be 15.1 mm+0.1 mm−0.0 mm, i.e. between 15.0 mm and 15.1 mm, the bottom edge of the centre hole may have a chamfer at an angle of 45° or this edge may be rounded off with a radius of not greater than 0.1 mm and the top edge of the centre hole may present burrs. Further, the bottom surface of the clamping area shall be flat within 0.1 mm and shall lay on reference plane P, the top surface of the clamping area shall be parallel to reference plane P within 0.2 mm and it defines reference plane Q, as indicated above. The height of the top surface of the reference plane P shall be 1.2 mm+0.3 mm−0.1 mm, i.e. between 1.1 mm and 1.5 mm. Further it is defined that the rim shall have a diameter of 120.0 mm±0.3 mm, i.e. between 119.7 mm and 120.3 mm and that in the zone extending between 117.7 mm to 118.3 mm and the rim the thickness of the disc is permitted to be higher than the height of the label above the reference plane P, which lays within the range of the height of the top surface above reference plane P, i.e. within the range of reference plane Q, or to decrease within certain ranges.
Further, standard ECMA-267 which is related to a 120 mm DVD-read-only disc defines the dimensional characteristics similar to that of general DVDs so that the disc shall have an overall diameter of 120.0 mm±0.3 mm, the centre hole of a substrate or a dummy substrate shall have a diameter of 15.0 mm+0.15 mm−0.0 mm, i.e. between 15.0 mm and 15.15 mm, wherein the diameter of the hole of an assemble disc, i.e. with both parts bonded together, shall be 15.0 mm min., that there shall be no burr on both edges of the centre hole and that the edge of the centre hole shall be rounded off or chamfered, wherein the rounding radius shall be 0.1 mm max and the chamfer shall extend over a height of 0.1 mm max. Further, it is defined that the clamping zone shall have a thickness of 1.2 mm+0.2 mm−0.1 mm, i.e. between 1.1 mm and 1.4 mm. It is also defined that within the rim area the outer edges of the disc shall be either rounded off with a rounding radius of 0.2 mm max. or be chamfered over within certain ranges.
Although it is defined for DVDs that the thickness of the disc, including adhesive layer, spacer(s) and label(s) shall be 1.20 mm+0.3 mm−0.06 mm, i.e. between 1.14 mm and 1.5 mm, and that also the height of the label of a CD above the reference plane P shall be 1.2 mm+0.3 mm−0.1 mm, i.e. between 1.1 mm and 1.5 mm, wherein the thickness of the transparent substrate shall be 1.2 mm±0.1 mm, i.e. between 1.1 mm and 1.3 mm with the bottom surface of the transparent substrate lying on the reference plane P, there is the tendency that the manufactured discs are as thin as possible to save polycarbonate material and time needed to cool the moulded substrates. Further, it is observed that the clamping areas lay generally in the plane of the information areas of the disc, although other configurations would be within the respective specifications, since such a configuration is easier to manufacture.
Hybrid discs, which comprise one DVD substrate and one CD substrate bonded together at their respective non-readable sides, i.e. so that the DVD substrate is read from one side and the CD substrate is read from the other side, show a height of approximately 1.8 mm, i.e. of a 1.2 mm CD substrate and a 0.6 mm half DVD substrate. Although it is the tendency to make such hybrid discs thinner to be within the 1.5 mm limit of maximum thickness allowed for CDs or DVDs, it is observed that many playback devices for CDs or DVDs show severe problems in handling such discs.